1. Field
The present invention relates to a diene elastomer modified by an alkoxysilane group, optionally partially or completely hydrolysed, bearing, if appropriate, another function capable of interacting with a reinforcing filler within a rubber composition. The present invention also relates to a reinforced rubber composition, which can be used in particular in the manufacture of tires, comprising this elastomer.
2. Description of Related Art
Now that savings in fuel and the need to protect the environment have become a priority, it is desirable to produce polymers having good mechanical properties and a hysteresis which is as low as possible in order to be able to process them in the form of rubber compositions which can be used in the manufacture of various semi-finished products participating in the forming of tires. Many solutions have already been experimented with in order to achieve the objective of fall in hysteresis. Mention may in particular be made of the modification of the structure of diene polymers and copolymers for the purpose of polymerization by means of functionalization agents, with the aim of obtaining a good interaction between the polymer, thus modified, and the filler, whether carbon black or a reinforcing inorganic filler. Provision has in particular been made to use diene polymers functionalized by alkoxysilane derivatives.
Mention may be made, by way of illustration of this prior art relating to reinforcing inorganic fillers, for example, of U.S. Pat. No. 5,066,721, which describes a rubber composition comprising a diene polymer functionalized by an alkoxysilane having at least one non-hydrolysable alkoxyl residue as a mixture with silica. Mention may also be made of Patent Application EP A 0 299 074, which describes functionalized polymers comprising alkoxysilane functions at the chain end. These functionalized polymers have been described in the prior art as effective in reducing hysteresis and improving abrasion resistance; however, their properties remain insufficient to allow the processing of these polymers in compositions intended to constitute treads of tires.
Provision has also been made to combine the functionalization by alkoxysilane functions with functionalization by other functions, in particular the amine function. Thus, Patent EP 0 992 537 describes a rubber composition which comprises an extended elastomer modified at the chain end by an alkoxysilane function and bearing, at the other end or along its chain, one or more amine functions. Furthermore, provision has also been made to improve the properties of rubber compositions by using elastomers functionalized at the chain end by alkoxysilane functions bearing an amine group, whether this is as black, silica or hybrid mixture. Mention may be made, for example, of Patent Application US 2005/0203251, which describes a rubber composition reinforced by silica comprising an elastomer functionalized at the chain end by an alkoxysilane bearing an amine group. Nevertheless, it turns out that the compositions comprising elastomers thus modified, whether black, silica or hybrid mixture, do not always exhibit a processing which is acceptable and a hysteresis which is satisfactory for use as tire tread.
The Applicant Companies have described, in the document WO 2009133068 A1, a functionalized diene elastomer essentially composed of the coupled entity of an elastomer having, within the chain, a group bearing an alkoxysilane function and an amine function, the silicon atom of this group bonding the two parts of the chain of the diene elastomer. This functionalized elastomer confers improved mechanical and dynamic properties on the composition in which it is present, in particular an improved hysteresis, while retaining a satisfactory raw processing, for the purpose in particular of use as tire tread.
It is an ongoing concern of designers of materials intended for the manufacture of tires to improve the compromise in mechanical and dynamic properties of the rubber compositions for the purpose of improving the performance of the tire in which they are present, without, however, damaging the stages of its manufacture or the properties of the elastomer. Thus, for example, the improvement in the compromise in properties must not be made to the detriment of the cold flow of the elastomer, which causes major disadvantages during the transportation and storage of rubbers.
Provision has already been made in the past to add elastomers coupled or star-branched using additional coupling or star-branching agents comprising tin or silicon in order to moderate the cold flow. Thus, for example, Patent Application WO 2009/077837 describes elastomers functionalized at each chain end in combination with elastomers which are star-branched, particularly by silicon. However, the combinations illustrated result in a reinforced rubber composition, the compromise in processing/hysteresis properties of which is not satisfactory for a tire application. The Applicant Companies have described, in Patent Application WO 2011/042507, a functionalized diene elastomer composed of a diene elastomer functionalized at one chain end by a silanol function and, in a certain proportion, of a coupled or star-branched diene elastomer based on tin. This elastomer confers, on a rubber composition in which it is present, hysteresis and processing properties which are entirely satisfactory and acceptable for tire use, while exhibiting a significantly improved resistance to cold flow.